Tainted reality

Its been known for some time that what we see depends on what we expect to see. That is the basis of illusions such as one to the right, which I took from Wikipedia. Square A is actually just the same shade of gray as square B.

BPS research digest reports on a related effect.

Karl Gegenfurtner and colleagues presented 14 participants with strangely coloured fruits – for example a pink banana – against a grey background. The participants’ task was to adjust the colour of the banana until it blended exactly with the grey background. It sounds easy, but the participants couldn’t do it because as they adjusted the colour, they compensated not just for the banana’s actual pink pigmentation, but also for a yellowness that only existed in their mind, thus leaving the banana with a slight bluish hue. That is, their memory for the typical colour of a banana was interfering with their performance.

By contrast, the participants didn’t have any trouble adjusting the colour of anonymous spots of light to make them blend in with the grey background – thus suggesting it wasn’t some quirk of the experimental set-up that was causing the participants difficulties with the fruit and veg.

Moreover, when presented with a banana that had been correctly adjusted to perfectly blend in with the grey background, the participants reported that it looked slightly yellow – a percept generated by their own mind, not by the actual colour of the banana.